The invention relates to a method and a device for providing a service between a service unit and terminal devices of at least one communication network.
There are currently two possibilities for providing services in a communication network:                The service is linked to the network technology, as, for example, a packet switching communication network, an IP network or a line switching communication network. A user can only use the service via a terminal device allocated to this communication network.        The service is not linked to a communication network. Thereby a user can access the contents of a service via terminal device supported by the service. As an example, one can look at a unified messaging service, where the user can retrieve messages via, for example, e-mail (Internet access and browser interface) or, for example, voice mail (PSTN, PLMN access, voice portal interface).        
Services that are fixed to a communication network, i.e. use the resources of the communication network, can only be usefully accessed via this communication network, and a user must register for this service via this communication network and the associated terminal device. If the user wants to use this service via different communication networks, then the user must register several times, separately via each communication network, and is not recognisable as one and the same user for the service. The service user specific data required for the services must be stored and maintained in different databases and in different formats in the databases depending on the signalling used and the network technology. From the service user's point of view, depending on the signalling and network technology used, that means several different services. This means a high level of effort and longer times for the provision both for the service provider as well as for the network operator. The service user must register for this service in each communication network, in which he wishes to use the service.